1. Field of the Invention
This invention relates generally to high-speed switching networks, and more particularly to a non-blocking high-speed switch.
2. Description of the Related Art
In the field of communications and data distribution, the need to switch greater numbers of signals at higher speeds has become increasingly important. State of the art switches must be able to accept a wide variety of signal formats in order to ensure compatibility between the systems interconnected via the switch. The signals can be analog or digital, processed or unprocessed. The signals can be centered at different frequencies with different band widths, and can be transmitted at different sampling rates with different word sizes. Current distribution schemes are inadequate to deal with the many existing signal formats and cannot easily grow to support future users.
Switch architectures, the heart of a wide band distribution network, have been an active area of research for over forty years. There are several design constraints which identify those characteristics desirable for an optimum switch network: the number of cross points required, the blocking or nonblocking characteristics, the degree of built-in redundancy, ease of control, and the need for interchannel rate synchronization.
Over the years, a number of switch architectures have been studied by authorities in this field. One commonly studied switch is a crossbar switch. In a crossbar switch, the inputs and outputs are arranged in a matrix array, with each input being tied to each output. The crossbar switch is non-blocking, asynchronous, and easily expandable. However, the number of cross points required to implement an N.times.N switch grows as N.sup.2. Also, there is only one path from any given input to any given output. Thus, a crossbar switch has no built in redundancy if an internal crosspoint fails. Another fairly well known switch, commonly referred to as the Clos switch, as disclosed in "A Study of Non-Blocking Switching Networks", the Bell System Technical Journal, Volume XXXII, March 1953, consists of a three-stage network which is one-to-one nonblocking and asynchronous. The Clos network has a significant advantage over a crossbar network in that it takes fewer crosspoints to implement a large switch array. Specifically, while an N.times.N crossbar switch grows as N.sup.2, a N.times.N Clos switch grows as 6N.sup.3/2 -3N. Also, the Clos network provides multiple paths from each input to each output, thereby building in redundancy. However, the broadcast capabilities of a Clos switch are limited, and it is not as easily expandable as is a crossbar network. Specifically, since the Clos switch is nonsymmetric, each configuration is unique. This means a complete reconfiguration is required when attempting to expand the switch.
In general, the ideal switch should require as few crosspoints as possible. This would reduce the size and complexity of the switch, as well as reduce the power requirements to operate the switch. Likewise, the need to ensure the switch is non-blocking and has built-in redundancy becomes self apparent: a blocked signal or signal switching failure due to an equipment failure decreases the switch's reliability and increases the risk that critical information may be lost.
The ideal switch should also be easy to control, since unduly complex control schemes make the system more difficult to expand and service. Relatedly, a switch reliant upon interchannel rate synchronization increases the complexity of the control scheme because clock characteristics must be preserved as the signal progresses through the switch.
It would therefore be advantageous to provide for a switch to be used in a wide band distribution system where the switch is nonblocking and has built in redundancy to reduce sensitivity to equipment failures. The switch should use as few crosspoints as possible to reduce the complexity of the switch, and should have a control scheme which is easily implemented. As such, the switch should be capable of switching asynchronous signals without needing interchannel rate synchronization. Also, the switch should be symmetric, allowing it to be expanded readily from basic switch elements rather than requiring a complete reconfiguration to expand its capacity. This allows switches to be constructed to suit particular needs without requiring unique switch designs for the various capacity requirements.